1. Field of the Invention
The present invention relates to a technology for charging a terminal device, and in particular to a charging technology for controlling a charging current to be supplied to a battery.
2. Description of the Related Art
Among rechargeable batteries, lithium ion batteries are attracting attention. The lithium ion battery has positive electrodes of lithium cobalt oxide (LiCoO2) and negative electrodes of graphite (carbon), and is configured so that the electrode plates are stacked in layers. Charge control for the lithium ion battery is such that a preliminary charge (pre-charge) is performed with a low current until the battery voltage exceeds a predetermined threshold, followed by a quick charge with a charging current higher than the preliminary charging current once the predetermined threshold has been exceeded (for example, see Japanese Patent Publication No. 3758361).
In some game systems, game controllers which communicate with game apparatuses by wireless means have been developed. The use of wireless game controllers makes it possible for users to freely play games from different positions. Conventional wired game controllers include some that have a mechanism for driving vibrating motors, thereby transmitting virtual vibrations during game play to the players. It is also desirable that wireless game controllers implement such vibrating motors. In general, the drive current required by a vibrating motor is higher than the system current that is consumed steadily by ICs inside a wireless game controller.
The battery of a wireless game controller is charged, for example, when connected to an external power supply through a universal serial bus (USB) cable or the like. When the battery charge level remaining becomes low during game play, the user connects the USB cable to the external power supply to charge the battery quickly while continuing the game. During this time, a drive request signal to the vibrating motor may sometimes be transmitted from the game apparatus, requesting that the vibrating motor be driven. It has thus been desired to develop a technology for performing efficient charge control for the battery even in these situations. Aside from the wireless game controllers that implement vibrating motors, the same need holds for other terminal devices that have loads to consume high currents sporadically during charging.